Editing Albedo

{{Short description|Ratio of how much light is reflected back from a body}}
{{Other uses}}
{{Use dmy dates|date=September 2019}}
[[File:Greenland_Albedo_Change.png|thumb|Albedo change in [[Greenland]]: the map shows the difference between the amount of sunlight [[Greenland]] reflected in the summer of 2011 versus the average percent it reflected between 2000 and 2006. Some areas reflect close to 20 percent less light than a decade ago.<ref name=":2">{{Cite web |date=2011 |title=Greenland's Ice Is Growing Darker |url=https://earthobservatory.nasa.gov/images/76916/greenlands-ice-is-growing-darker |access-date=6 July 2023 |website=NASA}}</ref>]]
'''Albedo''' ({{IPAc-en|æ|l|ˈ|b|iː|d|oʊ|audio=LL-Q1860 (eng)-Naomi Persephone Amethyst (NaomiAmethyst)-albedo.wav}} {{respell|al|BEE|doh}}; {{etymology|la|albedo|whiteness}}) is the fraction of [[sunlight]] that is [[Diffuse reflection|diffusely reflected]] by a body. It is measured on a scale from 0 (corresponding to a [[black body]] that absorbs all incident radiation) to 1 (corresponding to a body that reflects all incident radiation). ''Surface albedo'' is defined as the ratio of [[Radiosity (radiometry)|radiosity]] ''J''<sub>e</sub> to the [[irradiance]] ''E''<sub>e</sub> (flux per unit area) received by a surface.<ref>{{cite web|url=http://web.cse.ohio-state.edu/~parent.1/classes/782/Lectures/03_Radiometry.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://web.cse.ohio-state.edu/~parent.1/classes/782/Lectures/03_Radiometry.pdf |archive-date=2022-10-09 |url-status=live |title=Fundamentals of Rendering - Radiometry / Photometry|author1=Pharr|author2=Humphreys|website=Web.cse.ohio-state.edu|access-date=2 March 2022}}</ref> The proportion reflected is not only determined by properties of the surface itself, but also by the spectral and angular distribution of solar radiation reaching the Earth's surface.<ref>{{cite encyclopedia |url=http://curry.eas.gatech.edu/Courses/6140/ency/Chapter9/Ency_Atmos/Reflectance_Albedo_Surface.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://curry.eas.gatech.edu/Courses/6140/ency/Chapter9/Ency_Atmos/Reflectance_Albedo_Surface.pdf |archive-date=2022-10-09 |url-status=live |title=Reflectance and albedo, surface |encyclopedia=Encyclopedia of the Atmosphere |editor=J. R. Holton |editor2=J. A. Curry |last=Coakley |first=J. A. |publisher=Academic Press |year=2003|pages=1914–1923}}</ref> These factors vary with atmospheric composition, geographic location, and time (see [[position of the Sun]]).

While directional-hemispherical [[reflectance]] factor is calculated for a single angle of incidence (i.e., for a given position of the Sun), albedo is the directional integration of reflectance over all solar angles in a given period. The temporal resolution may range from seconds (as obtained from flux measurements) to daily, monthly, or annual averages.

Unless given for a specific wavelength (spectral albedo), albedo refers to the entire spectrum of solar radiation.<ref>{{cite journal |last1=Henderson-Sellers |first1=A. |last2=Wilson |first2=M. F.|year=1983 |quote=Albedo observations of the Earth's surface for climate research |jstor=37357 |journal=Philosophical Transactions of the Royal Society of London A |volume=309 |issue=1508 |title=The Study of the Ocean and the Land Surface from Satellites |pages=285–294 |bibcode=1983RSPTA.309..285H |doi=10.1098/rsta.1983.0042|s2cid=122094064 }}</ref> Due to measurement constraints, it is often given for the spectrum in which most solar energy reaches the surface (between 0.3 and 3 μm). This spectrum includes [[visible spectrum|visible light]] (0.4–0.7 μm), which explains why surfaces with a low albedo appear dark (e.g., trees absorb most radiation), whereas surfaces with a high albedo appear bright (e.g., snow reflects most radiation).

[[Ice–albedo feedback]] is a [[positive feedback]] climate process where a change in the area of [[ice caps]], [[glaciers]], and [[sea ice]] alters the albedo and surface temperature of a planet. [[Ice]] is very reflective, therefore it reflects far more solar energy back to space than the other types of land area or open water. Ice–albedo feedback plays an important role in global [[Climate change (general concept)|climate change]].<ref>{{Cite journal |last=Budyko |first=M. I. |date=1969-01-01 |title=The effect of solar radiation variations on the climate of the Earth |journal=Tellus |volume=21 |issue=5 |pages=611–619 |bibcode=1969Tell...21..611B |doi=10.3402/tellusa.v21i5.10109 |issn=0040-2826|doi-access=free }}</ref> Albedo is an important concept in [[climate science]].

==Terrestrial albedo==
{| class="wikitable floatright"
|+ Sample albedos
|-
! Surface
! Typical <br />albedo
|-
| Fresh asphalt || 0.04<ref name="heat island">{{cite web
 | last=Pon | first=Brian
 | date=30 June 1999
 | url=http://eetd.lbl.gov/HeatIsland/Pavements/Albedo/
 | title=Pavement Albedo | publisher=Heat Island Group
 | access-date=27 August 2007
 | archive-url= https://web.archive.org/web/20070829153207/http://eetd.lbl.gov/HeatIsland/Pavements/Albedo/
 | archive-date= 29 August 2007<!--Added by DASHBot-->
}}</ref>
|-
|Open ocean
|0.06<ref>{{cite web|url=https://nsidc.org/cryosphere/seaice/processes/albedo.html|title=Thermodynamics {{!}} Thermodynamics: Albedo {{!}} National Snow and Ice Data Center|website=nsidc.org|access-date=14 August 2016}}</ref>
|-
| Worn asphalt || 0.12<ref name="heat island" />
|-
| Conifer forest, <br />summer || 0.08,<ref name="Betts 1">{{Cite journal
 | author=Alan K. Betts
 | author2=John H. Ball
 | title=Albedo over the boreal forest
 | journal=Journal of Geophysical Research
 | date=1997
 | volume=102 | issue=D24 | pages=28,901–28,910
 | url=http://www.agu.org/pubs/crossref/1997/96JD03876.shtml
 | access-date=27 August 2007
 | doi=10.1029/96JD03876
 | bibcode=1997JGR...10228901B
 | archive-url=https://web.archive.org/web/20070930184719/http://www.agu.org/pubs/crossref/1997/96JD03876.shtml
 | archive-date=30 September 2007<!--Added by DASHBot-->
 | doi-access=free
}}</ref> 0.09 to 0.15<ref name="mmutrees" />
|-
| [[Deciduous forest]] || 0.15 to 0.18<ref name="mmutrees" />
|-
| Bare soil || 0.17<ref name="markvart">{{Cite book
  | author=Tom Markvart
  | author2=Luis CastaŁżer
  | date=2003
  | title=Practical Handbook of Photovoltaics: Fundamentals and Applications
  | publisher=Elsevier | isbn=978-1-85617-390-2
}}</ref>
|-
| Green grass || 0.25<ref name="markvart" />
|-
| Desert sand || 0.40<ref name="Tetzlaff">{{Cite book
 | first=G. | last=Tetzlaff | date=1983
 | title=Albedo of the Sahara
 |publisher=Cologne University Satellite Measurement of Radiation Budget Parameters
 | pages=60–63
}}</ref>
|-
| New concrete || 0.55<ref name="markvart" />
|-
| Ocean ice|| 0.50 to 0.70<ref name="markvart" />
|-
| Fresh snow || 0.80<ref name="markvart" />
|-
| [[Aluminium]] || 0.85<ref>{{cite journal | pmid=31822767 | pmc=6904492 | doi=10.1038/s41598-019-55272-x | title=The effects of surface albedo and initial lignin concentration on photodegradation of two varieties of Sorghum bicolor litter | journal=Scientific Reports | date=10 December 2019 | volume=9 | page=18748 | last1=Ruhland | first1=Christopher T. | last2=Niere | first2=Joshua A. | issue=1 | bibcode=2019NatSR...918748R }}</ref><ref>{{cite web | url=https://www.pvsyst.com/help/albedo.htm | title=Physical models used > Irradiation models > Albedo usual coefficients }}</ref>
|}
Any albedo in visible light falls within a range of about 0.9 for fresh snow to about 0.04 for charcoal, one of the darkest substances. Deeply shadowed cavities can achieve an effective albedo approaching the zero of a [[black body]]. When seen from a distance, the ocean surface has a low albedo, as do most forests, whereas desert areas have some of the highest albedos among landforms. Most land areas are in an albedo range of 0.1 to 0.4.<ref name="PhysicsWorld">{{cite web|url=http://scienceworld.wolfram.com/physics/Albedo.html |title=Albedo – from Eric Weisstein's World of Physics |publisher=Scienceworld.wolfram.com |access-date=19 August 2011}}</ref> The average albedo of [[Earth]] is about 0.3.<ref name="Goode" /> This is far higher than for the ocean primarily because of the contribution of clouds.

Earth's surface albedo is regularly estimated via [[Earth observation]] satellite sensors such as [[NASA]]'s [[MODIS]] instruments on board the [[Terra (satellite)|Terra]] and [[Aqua (satellite)|Aqua]] satellites, and the CERES instrument on the [[Suomi NPP]] and [[Joint Polar Satellite System|JPSS]]. As the amount of reflected radiation is only measured for a single direction by satellite, not all directions, a mathematical model is used to translate a sample set of satellite reflectance measurements into estimates of [[directional-hemispherical reflectance]] and bi-hemispherical reflectance (e.g.,<ref name="NASA" />). These calculations are based on the [[bidirectional reflectance distribution function]] (BRDF), which describes how the reflectance of a given surface depends on the view angle of the observer and the solar angle. BDRF can facilitate translations of observations of reflectance into albedo.{{citation needed|date=July 2023}}

Earth's average surface temperature due to its albedo and the [[greenhouse effect]] is currently about {{convert|15|C|F}}. If Earth were frozen entirely (and hence be more reflective), the average temperature of the planet would drop below {{convert|−40|C|F}}.<ref name="washington" /> If only the continental land masses became covered by glaciers, the mean temperature of the planet would drop to about {{convert|0|C|F}}.<ref name="clim-past" /> In contrast, if the entire Earth was covered by water – a so-called [[ocean planet]] – the average temperature on the planet would rise to almost {{convert|27|C|F}}.<ref name="Smith Robin" />

<!--===Variability and recent/spatiotemporal changes===-->
In 2021, scientists reported that Earth dimmed by ~0.5% over two decades (1998–2017) as measured by earthshine using modern photometric techniques. This may have both been co-caused by [[climate change]] as well as a substantial increase in global warming. However, the link to climate change has not been explored to date and it is unclear whether or not this represents an ongoing trend.<ref>{{cite news |last1=Gray |first1=Jennifer |title=The Earth isn't as bright as it once was |url=https://edition.cnn.com/2021/10/04/weather/earth-dimming-climate/index.html |access-date=19 October 2021 |work=CNN}}</ref><ref>{{cite journal |last1=Goode |first1=P. R. |last2=Pallé |first2=E. |last3=Shoumko |first3=A. |last4=Shoumko |first4=S. |last5=Montañes-Rodriguez |first5=P. |last6=Koonin |first6=S. E. |title=Earth's Albedo 1998–2017 as Measured From Earthshine |journal=Geophysical Research Letters |date=2021 |volume=48 |issue=17 |pages=e2021GL094888 |doi=10.1029/2021GL094888 |bibcode=2021GeoRL..4894888G |s2cid=239667126 |language=en |issn=1944-8007|doi-access=free }}</ref>

===White-sky, black-sky, and blue-sky albedo===
For land surfaces, it has been shown that the albedo at a particular [[solar zenith angle]] ''θ''<sub>''i''</sub> can be approximated by the proportionate sum of two terms:
* the [[directional-hemispherical reflectance]] at that solar zenith angle, <math>{\bar \alpha(\theta_i)}</math>, sometimes referred to as black-sky albedo, and
* the [[bi-hemispherical reflectance]], <math>\bar{ \bar \alpha}</math>, sometimes referred to as white-sky albedo.
with <math>{1-D}</math> being the proportion of direct radiation from a given solar angle, and <math>{D}</math> being the proportion of diffuse illumination, the actual albedo <math>{\alpha}</math> (also called blue-sky albedo) can then be given as:

:<math>\alpha = (1 - D) \bar\alpha(\theta_i) + D \bar{\bar\alpha}.</math>

This formula is important because it allows the albedo to be calculated for any given illumination conditions from a knowledge of the intrinsic properties of the surface.<ref name="BlueskyAlbedo" />

===Changes to albedo due to human activities===
[[File:2000- Albedo (reflectivity) of Earth.svg|thumb|Earth's albedo as monitored by the [[Clouds and the Earth's Radiant Energy System|CERES]] satellite system shows a darkening of Earth that has caused 1.7{{nbsp}}W/m<sup>2</sup> warming since 2010.<ref name=Hansen_20250203/> That amount, only some of which is [[Radiative forcing|climate forcing]], is equivalent to a 138 ppm increase of atmospheric carbon dioxide.<ref name=Hansen_20250203>{{cite journal |last1=Hansen |first1=James E. |last2=Kharecha |first2=Pushker |last3=Sato |first3=Makiko |last4=Tselioudis |first4=George |last5=Kelly |first5=Joseph |last6=Bauer |first6=Susanne E. |last7=Ruedy |first7=Reto |last8=Jeong |first8=Eunbi |last9=Jin |first9=Quijian |last10=Rignot |first10=Eric |last11=Velicogna |first11=Isabella |last12=Schoeberl |first12=Mark R. |last13=von Schuckmann |first13=Karina |last14=Amponsem |first14=Joshua |last15=Cao |first15=Junji |last16=Keskinen |first16=Anton |last17=Li |first17=Jing |last18=Pokela |first18=Anni |title=Global Warming Has Accelerated: Are the United Nations and the Public Well-Informed? |journal=Environment |date=3 February 2025 |volume=67 |issue=1 |pages=6–44 |doi=10.1080/00139157.2025.2434494|doi-access=free |bibcode=2025ESPSD..67....6H }} Figure 6.</ref>]]
[[File:ISS041-E-90107 - View of Spain.jpg|thumb|Greenhouses of El Ejido, Almería, Spain]]
Human activities (e.g., deforestation, farming, and urbanization) change the albedo of various areas around the globe.<ref>{{Cite journal |last1=Sagan |first1=Carl |last2=Toon |first2=Owen B. |last3=Pollack |first3=James B. |date=1979 |title=Anthropogenic Albedo Changes and the Earth's Climate |journal=Science |volume=206 |issue=4425 |pages=1363–1368 |bibcode=1979Sci...206.1363S |doi=10.1126/science.206.4425.1363 |issn=0036-8075 |jstor=1748990 |pmid=17739279 |s2cid=33810539}}</ref> [[Human impact on the environment|Human impacts]] to "the physical properties of the land surface can perturb the climate by altering the Earth’s radiative energy balance" even on a small scale or when undetected by satellites.<ref name=":0">{{Cite journal |last1=Campra |first1=Pablo |last2=Garcia |first2=Monica |last3=Canton |first3=Yolanda |last4=Palacios-Orueta |first4=Alicia |date=2008 |title=Surface temperature cooling trends and negative radiative forcing due to land use change toward greenhouse farming in southeastern Spain |journal=Journal of Geophysical Research |volume=113 |issue=D18 |bibcode=2008JGRD..11318109C |doi=10.1029/2008JD009912 |doi-access=free}}</ref>

[[Urbanization]] generally decreases albedo (commonly being 0.01–0.02 lower than adjacent [[croplands]]), which contributes to [[global warming]]. Deliberately increasing albedo in urban areas can mitigate the [[urban heat island]] effect. An estimate in 2022 found that on a global scale, "an albedo increase of 0.1 in worldwide urban areas would result in a cooling effect that is equivalent to absorbing ~44 [[Gigatons|Gt]] of CO<sub>2</sub> emissions."<ref>{{Cite journal |last1=Ouyang |first1=Zutao |last2=Sciusco |first2=Pietro |last3=Jiao |first3=Tong |last4=Feron |first4=Sarah |last5=Li |first5=Cheyenne |last6=Li |first6=Fei |last7=John |first7=Ranjeet |last8=Peilei |first8=Fan |last9=Li |first9=Xia |last10=Williams |first10=Christopher A. |last11=Chen |first11=Guangzhao |last12=Wang |first12=Chenghao |last13=Chen |first13=Jiquan |date=July 2022 |title=Albedo changes caused by future urbanization contribute to global warming |journal=Nature Communications |volume=13 |issue=1 |page=3800 |bibcode=2022NatCo..13.3800O |doi=10.1038/s41467-022-31558-z |pmc=9249918 |pmid=35778380}}</ref>

Intentionally enhancing the albedo of the Earth's surface, along with its daytime [[thermal emittance]], has been proposed as a [[Solar Radiation Management|solar radiation management]] strategy to mitigate [[Energy crisis|energy crises]] and global warming known as [[passive daytime radiative cooling]] (PDRC).<ref name=":1">{{Cite journal |last1=Wang |first1=Tong |last2=Wu |first2=Yi |last3=Shi |first3=Lan |last4=Hu |first4=Xinhua |last5=Chen |first5=Min |last6=Wu |first6=Limin |date=2021 |title=A structural polymer for highly efficient all-day passive radiative cooling |journal=Nature Communications |volume=12 |issue=365 |page=365 |doi=10.1038/s41467-020-20646-7 |pmc=7809060 |pmid=33446648 |quote=Accordingly, designing and fabricating efficient PDRC with sufficiently high solar reflectance (𝜌¯solar) (λ ~ 0.3–2.5 μm) to minimize solar heat gain and simultaneously strong LWIR thermal emittance (ε¯LWIR) to maximize radiative heat loss is highly desirable. When the incoming radiative heat from the Sun is balanced by the outgoing radiative heat emission, the temperature of the Earth can reach its steady state.}}</ref><ref name=":5">{{Cite journal |last1=Chen |first1=Meijie |last2=Pang |first2=Dan |last3=Chen |first3=Xingyu |last4=Yan |first4=Hongjie |last5=Yang |first5=Yuan |date=October 2021 |title=Passive daytime radiative cooling: Fundamentals, material designs, and applications |journal=EcoMat |volume=4 |doi=10.1002/eom2.12153 |s2cid=240331557 |quote=Passive daytime radiative cooling (PDRC) dissipates terrestrial heat to the extremely cold outer space without using any energy input or producing pollution. It has the potential to simultaneously alleviate the two major problems of energy crisis and global warming. |doi-access=free }}</ref><ref name=":02">{{Cite journal |last=Munday |first=Jeremy |date=2019 |title=Tackling Climate Change through Radiative Cooling |journal=Joule |volume=3 |issue=9 |pages=2057–2060 |doi=10.1016/j.joule.2019.07.010 |s2cid=201590290 |doi-access=free|bibcode=2019Joule...3.2057M }}</ref> Efforts toward widespread implementation of PDRCs may focus on maximizing the albedo of surfaces from very low to high values, so long as a thermal emittance of at least 90% can be achieved.<ref name=":22">{{Cite journal |last1=Anand |first1=Jyothis |last2=Sailor |first2=David J. |last3=Baniassadi |first3=Amir |date=February 2021 |title=The relative role of solar reflectance and thermal emittance for passive daytime radiative cooling technologies applied to rooftops |url=https://www.sciencedirect.com/science/article/abs/pii/S2210670720308295 |journal=Sustainable Cities and Society |volume=65 |page=102612 |doi=10.1016/j.scs.2020.102612 |bibcode=2021SusCS..6502612A |s2cid=229476136 |quote=Thus, as manufactures consider development of PDRC materials for building applications, their efforts should disproportionately focus on increasing surface solar reflectance (albedo) values, while retaining the conventional thermal emissivity. |via=Elsevier Science Direct}}</ref>

The tens of thousands of [[hectare]]s of greenhouses in [[Province of Almería|Almería, Spain]] form a large expanse of whitened plastic roofs. A 2008 study found that this anthropogenic change lowered the local surface area temperature of the high-albedo area, although changes were localized.<ref name=":0" /> A follow-up study found that "CO2-eq. emissions associated to changes in surface albedo are a consequence of land transformation" and can reduce surface temperature increases associated with climate change.<ref>{{Cite journal |last1=Muñoz |first1=Ivan |last2=Campra |first2=Pablo |date=2010 |title=Including CO2-emission equivalence of changes in land surface albedo in life cycle assessment. Methodology and case study on greenhouse agriculture |url=https://www.researchgate.net/publication/226490855 |journal=Int J Life Cycle Assess |volume=15 |issue=7 |pages=679–680 |bibcode=2010IJLCA..15..672M |doi=10.1007/s11367-010-0202-5 |s2cid=110705003 |via=Research Gate}}</ref>

==Examples of terrestrial albedo effects==
[[File:Albedo-e hg.svg|thumb|upright=1.3|The percentage of [[diffuse reflection|diffusely reflected]] [[sunlight]] relative to various surface conditions]]

=== Illumination ===
Albedo is not directly dependent on the illumination because changing the amount of incoming light proportionally changes the amount of reflected light, except in circumstances where a change in illumination induces a change in the Earth's surface at that location (e.g. through melting of reflective ice). However, albedo and illumination both vary by latitude. Albedo is highest near the poles and lowest in the subtropics, with a local maximum in the tropics.<ref name="Winston">{{cite journal| first=Jay |last=Winston |title=The Annual Course of Zonal Mean Albedo as Derived From ESSA 3 and 5 Digitized Picture Data |journal=Monthly Weather Review |volume=99 |pages=818–827| bibcode=1971MWRv...99..818W| date=1971| doi=10.1175/1520-0493(1971)099<0818:TACOZM>2.3.CO;2| issue=11|doi-access=free}}</ref>

===Insolation effects===
The intensity of albedo temperature effects depends on the amount of albedo and the level of local [[insolation]] ([[solar irradiance]]); high albedo areas in the [[Arctic]] and [[Antarctic]] regions are cold due to low insolation, whereas areas such as the [[Sahara Desert]], which also have a relatively high albedo, will be hotter due to high insolation. [[Tropical]] and [[sub-tropical]] [[rainforest]] areas have low albedo, and are much hotter than their [[temperate forest]] counterparts, which have lower insolation. Because insolation plays such a big role in the heating and cooling effects of albedo, high insolation areas like the tropics will tend to show a more pronounced fluctuation in local temperature when local albedo changes.<ref>{{cite web |title=Albedo Effect |url=https://www.npolar.no/en/fact/albedo/ |website=Norsk PolarInstitutt |publisher=Norwegian Polar Institute |access-date=23 June 2023}}</ref>

Arctic regions notably release more heat back into space than what they absorb, effectively cooling the [[Earth]]. This has been a concern since arctic ice and [[snow]] has been melting at higher rates due to higher temperatures, creating regions in the arctic that are notably darker (being water or ground which is darker color) and reflects less heat back into space. This [[Ice–albedo feedback|feedback loop]] results in a reduced albedo effect.<ref>{{Cite news|url=https://www.economist.com/news/briefing/21721364-commercial-opportunities-are-vastly-outweighed-damage-climate-thawing-arctic|title=The thawing Arctic threatens an environmental catastrophe|newspaper=The Economist|access-date=8 May 2017|date=29 April 2017}}</ref>

===Climate and weather===
{{See also|Climate change feedback}}
[[File:20220726 Feedbacks affecting global warming and climate change - block diagram.svg|thumb|right|upright=1.5| Some effects of global warming can either enhance ([[positive feedback]]s such as the ice-albedo feedback) or inhibit ([[negative feedback]]s) warming.<ref name=NASA_IntegratedSystem>{{cite web |title=The Study of Earth as an Integrated System |url=https://climate.nasa.gov/nasa_science/science/ |website=nasa.gov |publisher=NASA |date=2016 |archive-url=https://web.archive.org/web/20161102022200/https://climate.nasa.gov/nasa_science/science/ |archive-date=2 November 2016 |url-status=live }}</ref><ref name=IPCC_AR6_SGI_FigTS.17>Fig. TS.17, ''[https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_TS.pdf Technical Summary],'' Sixth Assessment Report (AR6), Working Group I, IPCC, 2021, p. 96. [https://web.archive.org/web/20220721021347/https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_TS.pdf Archived] from the original on 21 July 2022.</ref>]]
Albedo affects [[climate]] by determining how much [[radiation]] a planet absorbs.<ref>{{Cite book|url=https://books.google.com/books?id=av7q4N8Ib6sC&pg=PA53|title=Encyclopedia of Climate and Weather: Abs-Ero|last1=Schneider|first1=Stephen Henry|last2=Mastrandrea|first2=Michael D.|last3=Root|first3=Terry L.|date=2011|publisher=Oxford University Press|isbn=978-0-19-976532-4|page=53}}</ref> The uneven heating of Earth from albedo variations between land, ice, or ocean surfaces can drive [[weather]].<ref>{{Cite web |title=Albedo and Climate {{!}} Center for Science Education |url=https://scied.ucar.edu/learning-zone/how-climate-works/albedo-and-climate |access-date=2025-02-06 |website=scied.ucar.edu}}</ref>

The response of the climate system to an initial forcing is modified by feedbacks: increased by [[Positive feedback|"self-reinforcing" or "positive" feedbacks]] and reduced by [[Negative feedback|"balancing" or "negative" feedbacks]].<ref>{{cite web |year=2013 |title=The study of Earth as an integrated system |url=https://climate.nasa.gov/nasa_science/science/ |url-status=live |archive-url=https://web.archive.org/web/20190226190002/https://climate.nasa.gov/nasa_science/science/ |archive-date=26 February 2019 |series=Vitals Signs of the Planet |publisher=Earth Science Communications Team at NASA's Jet Propulsion Laboratory / California Institute of Technology}}</ref> The main reinforcing feedbacks are the [[Water vapour feedback|water-vapour feedback]], the [[ice–albedo feedback]], and the net effect of clouds.<ref>Arias, P.A., N. Bellouin, E. Coppola, R.G. Jones, G. Krinner, J. Marotzke, V. Naik, M.D. Palmer, G.-K. Plattner, J. Rogelj, M. Rojas, J. Sillmann, T. Storelvmo, P.W. Thorne, B. Trewin, K. Achuta Rao, B. Adhikary, R.P. Allan, K. Armour, G. Bala, R. Barimalala, S. Berger, J.G. Canadell, C. Cassou, A. Cherchi, W. Collins, W.D. Collins, S.L. Connors, S. Corti, F. Cruz, F.J. Dentener, C. Dereczynski, A. Di Luca, A. Diongue Niang, F.J. Doblas-Reyes, A. Dosio, H. Douville, F. Engelbrecht, V. Eyring, E. Fischer, P. Forster, B. Fox-Kemper, J.S. Fuglestvedt, J.C. Fyfe, et al., 2021: [https://www.ipcc.ch/report/ar6/wg1/chapter/technical-summary/ Technical Summary]. In ''[https://www.ipcc.ch/report/ar6/wg1/ Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change]'' [Masson-Delmotte, V., P. Zhai, A. Pirani, S.L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M.I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J.B.R. Matthews, T.K. Maycock, T. Waterfield, O. Yelekçi, R. Yu, and B. Zhou (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, pp. 33−144. doi: 10.1017/9781009157896.002.</ref>{{rp|58}}

===Albedo–temperature feedback===
{{Further|Ice–albedo feedback}}
When an area's albedo changes due to snowfall, a snow–temperature [[feedback]] results. A layer of snowfall increases local albedo, reflecting away sunlight, leading to local cooling. In principle, if no outside temperature change affects this area (e.g., a warm [[air mass]]), the raised albedo and lower temperature would maintain the current snow and invite further snowfall, deepening the snow–temperature feedback. However, because local [[weather]] is dynamic due to the change of [[season]]s, eventually warm air masses and a more direct angle of sunlight (higher [[insolation]]) cause melting. When the melted area reveals surfaces with lower albedo, such as grass, soil, or ocean, the effect is reversed: the darkening surface lowers albedo, increasing local temperatures, which induces more melting and thus reducing the albedo further, resulting in still more heating.

===Snow===
Snow albedo is highly variable, ranging from as high as 0.9 for freshly fallen snow, to about 0.4 for melting snow, and as low as 0.2 for dirty snow.<ref>{{cite book |last1=Hall |first1=Dorothy K. |author-link=Dorothy Hall (scientist)|title=Remote Sensing of Ice and Snow |date=1985 |publisher=Springer Netherlands |location=Dordrecht |isbn=978-94-009-4842-6}}</ref> Over [[Antarctica]], snow albedo averages a little more than 0.8. If a marginally snow-covered area warms, snow tends to melt, lowering the albedo, and hence leading to more snowmelt because more radiation is being absorbed by the snowpack (referred to as the [[Ice–albedo feedback|ice–albedo]] [[positive feedback]]).

In [[Switzerland]], the citizens have been protecting their glaciers with large white tarpaulins to slow down the ice melt. These large white sheets are helping to reject the rays from the sun and defecting the heat. Although this method is very expensive, it has been shown to work, reducing snow and ice melt by 60%.<ref>{{Cite web |last=swissinfo.ch/gw |date=2021-04-02 |title=Glacier tarpaulins an effective but expensive shield against heat |url=https://www.swissinfo.ch/eng/sci-&-tech/glacier-tarpaulins-an-effective-but-expensive-shield-against-heat/46501004 |access-date=2024-02-20 |website=SWI swissinfo.ch |language=en-GB}}</ref>

Just as fresh snow has a higher albedo than does dirty snow, the albedo of snow-covered sea ice is far higher than that of sea water. Sea water absorbs more [[solar radiation]] than would the same surface covered with reflective snow. When sea ice melts, either due to a rise in sea temperature or in response to increased solar radiation from above, the snow-covered surface is reduced, and more surface of sea water is exposed, so the rate of energy absorption increases. The extra absorbed energy heats the sea water, which in turn increases the rate at which sea ice melts. As with the preceding example of snowmelt, the process of melting of sea ice is thus another example of a positive feedback.<ref>"All About Sea Ice." National Snow and Ice Data Center. Accessed 16 November 2017. /cryosphere/seaice/index.html.</ref> Both positive feedback loops have long been recognized as important for [[global warming]].{{citation needed|date=January 2018}}

[[Cryoconite]], powdery windblown [[dust]] containing soot, sometimes reduces albedo on glaciers and ice sheets.<ref name="Nat. Geo">[http://ngm.nationalgeographic.com/2010/06/melt-zone/jenkins-text/3 "Changing Greenland – Melt Zone"] {{Webarchive|url=https://web.archive.org/web/20160303175416/http://ngm.nationalgeographic.com/2010/06/melt-zone/jenkins-text/3 |url2=https://archive.wikiwix.com/cache/20110806084123/http://ngm.nationalgeographic.com/2010/06/melt-zone/jenkins-text/3 |date=3 March 2016 |date2= 6 August 2011}} page 3, of 4, article by Mark Jenkins in ''[[National Geographic (magazine)|National Geographic]]'' June 2010, accessed 8 July 2010</ref>

The dynamical nature of albedo in response to positive feedback, together with the effects of small errors in the measurement of albedo, can lead to large errors in energy estimates. Because of this, in order to reduce the error of energy estimates, it is important to measure the albedo of snow-covered areas through [[remote sensing]] techniques rather than applying a single value for albedo over broad regions.{{citation needed|date=January 2018}}

===Small-scale effects===
Albedo works on a smaller scale, too. In sunlight, dark clothes absorb more heat and light-coloured clothes reflect it better, thus allowing some control over body temperature by exploiting the albedo effect of the colour of external clothing.<ref name="ranknfile-ue">{{cite web|url=http://www.ranknfile-ue.org/h&s0897.html |title=Health and Safety: Be Cool! (August 1997) |publisher=Ranknfile-ue.org |access-date=19 August 2011}}</ref>

=== Solar photovoltaic effects ===
Albedo can affect the [[electrical energy]] output of solar [[photovoltaic system|photovoltaic devices]]. For example, the effects of a spectrally responsive albedo are illustrated by the differences between the spectrally weighted albedo of solar photovoltaic technology based on hydrogenated amorphous silicon (a-Si:H) and crystalline silicon (c-Si)-based compared to traditional spectral-integrated albedo predictions. Research showed impacts of over 10% for vertically (90°) mounted systems, but such effects were substantially lower for systems with lower surface tilts.<ref>{{cite journal | last1 = Andrews | first1 = Rob W. | last2 = Pearce | first2 = Joshua M. | date = 2013 | title = The effect of spectral albedo on amorphous silicon and crystalline silicon solar photovoltaic device performance | journal = Solar Energy | volume = 91 | pages = 233–241 | doi = 10.1016/j.solener.2013.01.030 |bibcode = 2013SoEn...91..233A | url = https://www.academia.edu/3081684 }}</ref> Spectral albedo strongly affects the performance of [[bifacial solar cells]] where rear surface performance gains of over 20% have been observed for c-Si cells installed above healthy vegetation.<ref>{{cite journal | last1 = Riedel-Lyngskær | first1 = Nicholas| last2 = Ribaconka | first2 = Ribaconka | last3 = Po | first3 = Mario | last4 = Thorseth | first4 = Anders | last5 = Thorsteinsson | first5 = Sune | last6 = Dam-Hansen | first6 = Carsten | last7 = Jakobsen | first7 = Michael L. | date = 2022| title = The effect of spectral albedo in bifacial photovoltaic performance | journal = Solar Energy | volume = 231| pages = 921–935 | doi = 10.1016/j.solener.2021.12.023 | bibcode = 2022SoEn..231..921R| s2cid = 245488941| doi-access = free }}</ref> An analysis on the bias due to the specular reflectivity of 22 commonly occurring surface materials (both human-made and natural) provided effective albedo values for simulating the performance of seven photovoltaic materials mounted on three common photovoltaic system topologies: industrial (solar farms), commercial flat rooftops and residential pitched-roof applications.<ref>{{cite journal | last1 = Brennan | first1 = M.P. | author-link4 = J. M. Pearce | last2 = Abramase | first2 = A.L. | last3 = Andrews | first3 = R.W. | last4 = Pearce | first4 = J. M. | date = 2014 | title = Effects of spectral albedo on solar photovoltaic devices | journal = Solar Energy Materials and Solar Cells | volume = 124 | pages = 111–116 | doi = 10.1016/j.solmat.2014.01.046 | bibcode = 2014SEMSC.124..111B | url = https://www.academia.edu/6222506 }}</ref>

===Trees===
{{Update section|date=March 2023|reason=the references used are quite old; there must be more updated information available in the [[IPCC Sixth Assessment Report]]}}
{{See also|Climate change#Land surface changes}}
Forests generally have a low albedo because the majority of the ultraviolet and [[visible spectrum]] is absorbed through [[photosynthesis]]. For this reason, the greater heat absorption by trees could offset some of the carbon benefits of [[afforestation]] (or offset the negative climate impacts of [[deforestation]]). In other words: The [[climate change mitigation]] effect of [[carbon sequestration]] by forests is partially counterbalanced in that [[reforestation]] can decrease the reflection of sunlight (albedo).<ref>{{cite journal |last1=Zhao |first1=Kaiguang |last2=Jackson |first2=Robert B |title=Biophysical forcings of land-use changes from potential forestry activities in North America |journal=Ecological Monographs |date=2014 |volume=84 |issue=2 |pages=329–353 |doi=10.1890/12-1705.1 |bibcode=2014EcoM...84..329Z |s2cid=56059160 |url=https://jacksonlab.stanford.edu/sites/g/files/sbiybj20871/files/media/file/em2014.pdf}}</ref>

In the case of evergreen forests with seasonal snow cover, albedo reduction may be significant enough for deforestation to cause a net cooling effect.<ref name="Betts" /> Trees also impact climate in extremely complicated ways through [[evapotranspiration]]. The water vapor causes cooling on the land surface, causes heating where it condenses, acts as strong greenhouse gas, and can increase albedo when it condenses into clouds.<ref>{{cite journal | last1 = Boucher | date = 2004 | title = Direct human influence of irrigation on atmospheric water vapour and climate | journal = Climate Dynamics | volume = 22 | issue = 6–7| pages = 597–603 | doi=10.1007/s00382-004-0402-4|display-authors=etal|bibcode = 2004ClDy...22..597B | s2cid = 129640195 | url = https://www.academia.edu/25329256}}</ref> Scientists generally treat evapotranspiration as a net cooling impact, and the net climate impact of albedo and evapotranspiration changes from deforestation depends greatly on local climate.<ref>{{cite journal | last1 = Bonan | first1 = GB | date = 2008 | title = Forests and Climate Change: Forcings, Feedbacks, and the Climate Benefits of Forests | journal = Science | volume = 320 | issue = 5882| pages = 1444–1449 | doi = 10.1126/science.1155121 | pmid=18556546|bibcode = 2008Sci...320.1444B  | s2cid = 45466312 | url = https://zenodo.org/record/1230896 }}</ref>

Mid-to-high-latitude forests have a much lower albedo during snow seasons than flat ground, thus contributing to warming. Modeling that compares the effects of albedo differences between forests and grasslands suggests that expanding the land area of forests in temperate zones offers only a temporary mitigation benefit.<ref>{{cite web |author=Jonathan Amos |date=15 December 2006 |title=Care needed with carbon offsets |url=http://news.bbc.co.uk/1/hi/sci/tech/6184577.stm |access-date=8 July 2008 |publisher=BBC}}</ref><ref>{{cite web |date=5 December 2005 |title=Models show growing more forests in temperate regions could contribute to global warming |url=https://publicaffairs.llnl.gov/news/news_releases/2005/NR-05-12-04.html |url-status=dead |archive-url=https://web.archive.org/web/20100527212654/https://publicaffairs.llnl.gov/news/news_releases/2005/NR-05-12-04.html |archive-date=27 May 2010 |access-date=8 July 2008 |publisher=Lawrence Livermore National Laboratory}}</ref><ref>{{cite journal |author1=S. Gibbard |author2=K. Caldeira |author3=G. Bala |author4=T. J. Phillips |author5=M. Wickett |date=December 2005 |title=Climate effects of global land cover change |url=https://digital.library.unt.edu/ark:/67531/metadc874513/ |journal=Geophysical Research Letters |volume=32 |issue=23 |pages=L23705 |bibcode=2005GeoRL..3223705G |doi=10.1029/2005GL024550 |doi-access=free}}</ref><ref>{{cite journal |last1=Malhi |first1=Yadvinder |last2=Meir |first2=Patrick |last3=Brown |first3=Sandra |year=2002 |title=Forests, carbon and global climate |journal=Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences |volume=360 |issue=1797 |pages=1567–91 |bibcode=2002RSPTA.360.1567M |doi=10.1098/rsta.2002.1020 |pmid=12460485 |s2cid=1864078}}</ref>

In seasonally snow-covered zones, winter albedos of treeless areas are 10% to 50% higher than nearby forested areas because snow does not cover the trees as readily. [[Deciduous trees]] have an albedo value of about 0.15 to 0.18 whereas [[coniferous trees]] have a value of about 0.09 to 0.15.<ref name="mmutrees" /> Variation in summer albedo across both forest types is associated with maximum rates of photosynthesis because plants with high growth capacity display a greater fraction of their foliage for direct interception of incoming radiation in the upper canopy.<ref name="Ollinger">{{cite journal
| title = Canopy nitrogen, carbon assimilation and albedo in temperate and boreal forests: Functional relations and potential climate feedbacks
| journal = Proceedings of the National Academy of Sciences
| volume = 105
| issue = 49
| date = 2008
| url= | last1 = Ollinger
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| doi-access = free
}}</ref> The result is that wavelengths of light not used in photosynthesis are more likely to be reflected back to space rather than being absorbed by other surfaces lower in the canopy.

Studies by the [[Hadley Centre]] have investigated the relative (generally warming) effect of albedo change and (cooling) effect of [[carbon sequestration]] on planting forests. They found that new forests in tropical and midlatitude areas tended to cool; new forests in high latitudes (e.g., Siberia) were neutral or perhaps warming.<ref name="Betts" />

Research in 2023, drawing from 176 flux stations globally, revealed a climate trade-off: increased carbon uptake from [[afforestation]] results in reduced albedo. Initially, this reduction may lead to moderate global warming over a span of approximately 20 years, but it is expected to transition into significant cooling thereafter.<ref>{{Cite journal |last1=Graf |first1=Alexander |last2=Wohlfahrt |first2=Georg |last3=Aranda-Barranco |first3=Sergio |last4=Arriga |first4=Nicola |last5=Brümmer |first5=Christian |last6=Ceschia |first6=Eric |last7=Ciais |first7=Philippe |last8=Desai |first8=Ankur R. |last9=Di Lonardo |first9=Sara |last10=Gharun |first10=Mana |last11=Grünwald |first11=Thomas |last12=Hörtnagl |first12=Lukas |last13=Kasak |first13=Kuno |last14=Klosterhalfen |first14=Anne |last15=Knohl |first15=Alexander |date=2023-08-25 |title=Joint optimization of land carbon uptake and albedo can help achieve moderate instantaneous and long-term cooling effects |journal=Communications Earth & Environment |language=en |volume=4 |issue=1 |page=298 |doi=10.1038/s43247-023-00958-4 |pmid=38665193 |pmc=11041785 |bibcode=2023ComEE...4..298G |issn=2662-4435 |hdl-access=free |hdl=10481/85323}}</ref>

===Water===
[[File:water reflectivity.jpg|thumb|upright=1.3|Reflectivity of smooth water at {{convert|20|C|F}} (refractive index=1.333)]]
Water reflects light very differently from typical terrestrial materials. The reflectivity of a water surface is calculated using the [[Fresnel equations]].

At the scale of the wavelength of light even wavy water is always smooth so the light is reflected in a locally [[specular reflection|specular manner]] (not [[Diffuse reflection|diffusely]]). The glint of light off water is a commonplace effect of this. At small [[angle of incidence (optics)|angles of incident]] light, [[waviness]] results in reduced reflectivity because of the steepness of the reflectivity-vs.-incident-angle curve and a locally increased average incident angle.<ref name="Fresnel" />

Although the reflectivity of water is very low at low and medium angles of incident light, it becomes very high at high angles of incident light such as those that occur on the illuminated side of Earth near the [[terminator (solar)|terminator]] (early morning, late afternoon, and near the poles). However, as mentioned above, waviness causes an appreciable reduction. Because light specularly reflected from water does not usually reach the viewer, water is usually considered to have a very low albedo in spite of its high reflectivity at high angles of incident light.

Note that white caps on waves look white (and have high albedo) because the water is foamed up, so there are many superimposed bubble surfaces which reflect, adding up their reflectivities. Fresh 'black' ice exhibits Fresnel reflection.
Snow on top of this sea ice increases the albedo to 0.9.<ref>{{Cite web |date=2007-01-31 |title=Arctic Reflection: Clouds Replace Snow and Ice as Solar Reflector |url=https://earthobservatory.nasa.gov/features/ArcticReflector/arctic_reflector4.php |access-date=2022-04-28 |website=earthobservatory.nasa.gov |language=en}}</ref>

===Clouds===
[[Cloud albedo]] has substantial influence over atmospheric temperatures. Different types of clouds exhibit different reflectivity, theoretically ranging in albedo from a minimum of near 0 to a maximum approaching 0.8. "On any given day, about half of Earth is covered by clouds, which reflect more sunlight than land and water. Clouds keep Earth cool by reflecting sunlight, but they can also serve as blankets to trap warmth."<ref name="livescience">{{cite web|url=http://www.livescience.com/environment/060124_earth_albedo.html |title=Baffled Scientists Say Less Sunlight Reaching Earth |publisher=LiveScience |date=24 January 2006 |access-date=19 August 2011}}</ref>

Albedo and climate in some areas are affected by artificial clouds, such as those created by the [[contrail]]s of heavy commercial airliner traffic.<ref>{{cite journal|title=Contrails reduce daily temperature range|url=http://facstaff.uww.edu/travisd/pdf/jetcontrailsrecentresearch.pdf|journal=Nature |access-date=7 July 2015|archive-url=https://web.archive.org/web/20060503192714/http://facstaff.uww.edu/travisd/pdf/jetcontrailsrecentresearch.pdf|archive-date=3 May 2006|page=601|volume=418|issue=6898|date=8 August 2002|url-status=dead|doi=10.1038/418601a|bibcode = 2002Natur.418..601T|pmid=12167846|last1=Travis|first1=D. J.|last2=Carleton|first2=A. M.|last3=Lauritsen|first3=R. G.|s2cid=4425866}}</ref> A study following the burning of the Kuwaiti oil fields during Iraqi occupation showed that temperatures under the burning oil fires were as much as {{convert|10|C-change|0}} colder than temperatures several miles away under clear skies.<ref name="harvard">{{cite journal |title=The Kuwait oil fires as seen by Landsat |date=30 May 1991|bibcode=1992JGR....9714565C |last1=Cahalan |first1=Robert F. |volume=97 |issue=D13 |page=14565 |journal=Journal of Geophysical Research: Atmospheres |doi=10.1029/92JD00799|url=https://www.researchgate.net/publication/23842551 }}</ref>

===Aerosol effects===
[[Aerosols]] (very fine particles/droplets in the atmosphere) have both direct and indirect effects on Earth's radiative balance. The direct (albedo) effect is generally to cool the planet; the indirect effect (the particles act as [[cloud condensation nuclei]] and thereby change cloud properties) is less certain.<ref name="girda">{{cite web|url=http://www.grida.no/climate/ipcc_tar/wg1/231.htm#671 |title=Climate Change 2001: The Scientific Basis |publisher=Grida.no |access-date=19 August 2011| archive-url= https://web.archive.org/web/20110629175429/http://www.grida.no/climate/ipcc_tar/wg1/231.htm| archive-date= 29 June 2011<!--Added by DASHBot-->}}</ref>

===Black carbon===
Another albedo-related effect on the climate is from [[black carbon]] particles. The size of this effect is difficult to quantify: the [[Intergovernmental Panel on Climate Change]] estimates that the global mean [[radiative forcing]] for black carbon aerosols from fossil fuels is +0.2 W m<sup>−2</sup>, with a range +0.1 to +0.4 W m<sup>−2</sup>.<ref name="girda 1">{{cite web|url=http://www.grida.no/climate/ipcc_tar/wg1/233.htm |title=Climate Change 2001: The Scientific Basis |publisher=Grida.no |access-date=19 August 2011| archive-url= https://web.archive.org/web/20110629180154/http://www.grida.no/climate/ipcc_tar/wg1/233.htm| archive-date= 29 June 2011<!--Added by DASHBot-->}}</ref> Black carbon is a bigger cause of the melting of the polar ice cap in the Arctic than carbon dioxide due to its effect on the albedo.<ref>James Hansen & Larissa Nazarenko, ''Soot Climate Forcing Via Snow and Ice Albedos'', 101 Proc. of the Nat'l. Acad. of Sci. 423 (13 January 2004) ("The efficacy of this forcing is »2 (i.e., for a given forcing it is twice as effective as CO<sub>2</sub> in altering global surface air temperature)"); ''compare'' Zender Testimony, ''supra'' note 7, at 4 (figure 3); See J. Hansen & L. Nazarenko, ''supra'' note 18, at 426. ("The efficacy for changes of Arctic sea ice albedo is >3. In additional runs not shown here, we found that the efficacy of albedo changes in Antarctica is also >3."); ''See also'' Flanner, M.G., C.S. Zender, J.T. Randerson, and P.J. Rasch, ''Present-day climate forcing and response from black carbon in snow'', 112 J. GEOPHYS. RES. D11202 (2007) ("The forcing is maximum coincidentally with snowmelt onset, triggering strong snow-albedo feedback in local springtime. Consequently, the "efficacy" of black carbon/snow forcing is more than three times greater than forcing by CO<sub>2</sub>.").</ref>{{Failed verification|date=January 2020}}

== Astronomical albedo ==
[[File:Titan and Saturn - May 6 2012 - combined (35516187116).jpg|thumb|upright=1.2|The moon [[Titan (moon)|Titan]] is darker than [[Saturn]] even though they receive the same amount of sunlight. This is due to a difference in albedo (0.22 versus 0.499 in [[geometric albedo]]).]]In astronomy, the term '''albedo''' can be defined in several different ways, depending upon the application and the wavelength of electromagnetic radiation involved.

===Optical or visual albedo===
The albedos of [[planet]]s, [[Natural satellite|satellites]] and [[minor planet]]s such as [[asteroid]]s can be used to infer much about their properties. The study of albedos, their dependence on wavelength, lighting angle ("phase angle"), and variation in time composes a major part of the astronomical field of [[photometry (astronomy)|photometry]]. For small and far objects that cannot be resolved by telescopes, much of what we know comes from the study of their albedos. For example, the absolute albedo can indicate the surface ice content of outer [[Solar System]] objects, the variation of albedo with phase angle gives information about [[regolith]] properties, whereas unusually high radar albedo is indicative of high metal content in [[asteroid]]s.

[[Enceladus]], a moon of Saturn, has one of the highest known optical albedos of any body in the Solar System, with an albedo of 0.99. Another notable high-albedo body is [[Eris (dwarf planet)|Eris]], with an albedo of 0.96.<ref name="sicardy">
{{cite journal
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</ref> Many small objects in the outer Solar System<ref name="tnoalbedo">{{cite web
  |date=17 September 2008
  |title=TNO/Centaur diameters and albedos
  |publisher=Johnston's Archive
  |author=Wm. Robert Johnston
  |url=http://www.johnstonsarchive.net/astro/tnodiam.html
  |access-date=17 October 2008| archive-url= https://web.archive.org/web/20081022223827/http://www.johnstonsarchive.net/astro/tnodiam.html| archive-date= 22 October 2008<!--Added by DASHBot-->}}</ref> and [[asteroid belt]] have low albedos down to about 0.05.<ref name="astalbedo">{{cite web
  |date=28 June 2003
  |title=Asteroid albedos: graphs of data
  |publisher=Johnston's Archive
  |author=Wm. Robert Johnston
  |url=http://www.johnstonsarchive.net/astro/astalbedo.html
  |access-date=16 June 2008| archive-url= https://web.archive.org/web/20080517100307/http://www.johnstonsarchive.net/astro/astalbedo.html| archive-date= 17 May 2008<!--Added by DASHBot-->}}</ref> A typical [[comet nucleus]] has an albedo of 0.04.<ref name="dark">{{cite news
  |date=29 November 2001
  |title=Comet Borrelly Puzzle: Darkest Object in the Solar System
  |work=Space.com
  |author=Robert Roy Britt
  |url=http://www.space.com/scienceastronomy/solarsystem/borrelly_dark_011129.html
  |access-date=1 September 2012| archive-url= https://web.archive.org/web/20090122074028/http://www.space.com/scienceastronomy/solarsystem/borrelly_dark_011129.html| archive-date= 22 January 2009}}</ref> Such a dark surface is thought to be indicative of a primitive and heavily [[space weathering|space weathered]] surface containing some [[organic compound]]s.

The overall albedo of the [[Moon]] is measured to be around 0.14,<ref name="CERESmoon">
{{cite journal
| title = Celestial body irradiance determination from an underfilled satellite radiometer: application to albedo and thermal emission measurements of the Moon using CERES
| journal = Applied Optics
| volume = 47 | issue = 27
| date = 2008
| bibcode = 2008ApOpt..47.4981M
| last1 = Matthews
| first1 = G.
| pages = 4981–4993
|doi = 10.1364/AO.47.004981
| pmid=18806861}}
</ref> but it is strongly directional and non-[[Lambertian reflectance|Lambertian]], displaying also a strong [[opposition effect]].<ref name="medkeff" /> Although such reflectance properties are different from those of any terrestrial terrains, they are typical of the [[regolith]] surfaces of airless Solar System bodies.

Two common optical albedos that are used in astronomy are the (V-band) [[geometric albedo]] (measuring brightness when illumination comes from directly behind the observer) and the [[Bond albedo]] (measuring total proportion of electromagnetic energy reflected). Their values can differ significantly, which is a common source of confusion.

{| class="wikitable"
|-
! Planet
! Geometric
! Bond
|-
| Mercury
| 0.142 <ref name="Mallama_et_al"/>
| 0.088 <ref name="Mallama"/> or 0.068
|-
| Venus
| 0.689 <ref name="Mallama_et_al"/>
| 0.76  <ref name="Haus_et_al"/> or 0.77
|-
| Earth
| 0.434 <ref name="Mallama_et_al"/>
| 0.294 <ref>{{cite web|url =http://nssdc.gsfc.nasa.gov/planetary/factsheet/earthfact.html |title =Earth Fact Sheet|website = NASA|first = David R.|last = Williams |date = 11 January 2024}}</ref>
|-
| Mars
| 0.170 <ref name="Mallama_et_al"/>
| 0.250 <ref>{{cite web|url = http://nssdc.gsfc.nasa.gov/planetary/factsheet/marsfact.html |title =Mars Fact Sheet|website = NASA|first = David R.|last = Williams |date = 25 November 2020}}</ref>
|-
| Jupiter
| 0.538 <ref name="Mallama_et_al"/>
| 0.343±0.032 <ref>{{cite web|url = http://nssdc.gsfc.nasa.gov/planetary/factsheet/jupiterfact.html |title =Jupiter Fact Sheet|website = NASA|first = David R.|last = Williams |date = 11 January 2024}}</ref> and also 0.503±0.012 <ref name="Li_et_al"/>
|-
| Saturn
| 0.499 <ref name="Mallama_et_al"/>
| 0.342 <ref name="Hanel_et_al"/>
|-
| Uranus
| 0.488 <ref name="Mallama_et_al"/>
| 0.300 <ref name="Pearl_et_al_Uranus"/>
|-
| Neptune
| 0.442 <ref name="Mallama_et_al"/>
| 0.290 <ref name="Pearl_et_al_Neptune"/>
|}

In detailed studies, the directional reflectance properties of astronomical bodies are often expressed in terms of the five [[Hapke parameters]] which semi-empirically describe the variation of albedo with [[phase angle (astronomy)|phase angle]], including a characterization of the opposition effect of [[regolith]] surfaces. One of these five parameters is yet another type of albedo called the [[single-scattering albedo]]. It is used to define scattering of electromagnetic waves on small particles. It depends on properties of the material ([[refractive index]]), the size of the particle, and the wavelength of the incoming radiation.

An important relationship between an object's astronomical (geometric) albedo, [[Absolute magnitude#Absolute magnitude for planets (H)|absolute magnitude]] and diameter is given by:<ref name="bruton">{{cite web
 |title=Conversion of Absolute Magnitude to Diameter for Minor Planets
 |publisher=Department of Physics & Astronomy (Stephen F. Austin State University)
 |author=Dan Bruton
 |url=http://www.physics.sfasu.edu/astro/asteroids/sizemagnitude.html
 |access-date=7 October 2008
 |archive-url=https://web.archive.org/web/20081210190134/http://www.physics.sfasu.edu/astro/asteroids/sizemagnitude.html
 |archive-date=10 December 2008
 |url-status=dead
}}</ref>
<math display="block">A =\left ( \frac{1329\times10^{-H/5}}{D} \right ) ^2,</math>
where <math>A</math> is the astronomical albedo, <math>D</math> is the diameter in kilometers, and <math>H</math> is the absolute magnitude.

===Radar albedo===
In planetary [[radar astronomy]], a microwave (or radar) pulse is transmitted toward a planetary target (e.g. Moon, asteroid, etc.) and the echo from the target is measured. In most instances, the transmitted pulse is [[circular polarization|circularly polarized]] and the received pulse is measured in the same sense of polarization as the transmitted pulse (SC) and the opposite sense (OC).<ref name="Ostro_Planetary_Radar">{{cite book |last1=Ostro |first1=S. J. |editor1-last=McFadden |editor1-first=L. |editor2-last=Weissman |editor2-first=P. R. |editor3-last=Johnson |editor3-first=T. V. |title=Planetary Radar in Encyclopedia of the Solar System |date=2007 |publisher=Academic Press |isbn=978-0-12-088589-3 |pages=735–764 |edition=2nd}}</ref><ref name="Ostro_Asteroid_Radar">{{cite book |last1=Ostro |first1=S. J. |display-authors=etal |editor1-last=Bottke |editor1-first=W. |editor2-last=Cellino |editor2-first=A. |editor3-last=Paolicchi |editor3-first=P. |editor4-last=Binzel |editor4-first=R. P. |title=Asteroid Radar Astronomy in Asteroids III |date=2002 |publisher=University of Arizona Press |isbn=9780816522811 |pages=151–168}}</ref> The echo power is measured in terms of [[radar cross-section]], <math>{\sigma}_{OC}</math>, <math>{\sigma}_{SC}</math>, or <math>{\sigma}_{T}</math> (total power, SC + OC) and is equal to the cross-sectional area of a metallic sphere (perfect reflector) at the same distance as the target that would return the same echo power.<ref name="Ostro_Planetary_Radar" />

Those components of the received echo that return from first-surface reflections (as from a smooth or mirror-like surface) are dominated by the OC component as there is a reversal in polarization upon reflection. If the surface is rough at the wavelength scale or there is significant penetration into the regolith, there will be a significant SC component in the echo caused by multiple scattering.<ref name="Ostro_Asteroid_Radar" />

For most objects in the solar system, the OC echo dominates and the most commonly reported radar albedo parameter is the (normalized) OC radar albedo (often shortened to radar albedo):<ref name="Ostro_Planetary_Radar" />
<math display="block"> \hat{\sigma}_\text{OC} = \frac{{\sigma}_\text{OC}}{\pi r^2} </math>

where the denominator is the effective cross-sectional area of the target object with mean radius, <math>r</math>. A smooth metallic sphere would have <math>\hat{\sigma}_\text{OC} = 1</math>.

====Radar albedos of Solar System objects====

{| class="wikitable"
|-
! Object
! <math>\hat{\sigma}_\text{OC}</math>
|-
| Moon
| 0.06 <ref name="Ostro_Planetary_Radar" />
|-
| Mercury
| 0.05 <ref name="Ostro_Planetary_Radar" />
|-
| Venus
| 0.10 <ref name="Ostro_Planetary_Radar" />
|-
| Mars
| 0.06 <ref name="Ostro_Planetary_Radar" />
|-
| Avg. S-type asteroid
| 0.14 <ref name="Magri2007">{{cite journal |last1=Magri |first1=C | display-authors=etal |title=A radar survey of main-belt asteroids: Arecibo observations of 55 objects during 1999-2004 |journal=Icarus |date=2007 |volume=186 |issue=1 |pages=126–151 |doi=10.1016/j.icarus.2006.08.018|bibcode=2007Icar..186..126M }}</ref>
|-
| Avg. C-type asteroid
| 0.13 <ref name="Magri2007"/>
|-
| Avg. M-type asteroid
| 0.26 <ref name="Shepard et al 2015">{{cite journal |last1=Shepard |first1=M. K. | display-authors= etal |title=A radar survey of M- and X-class asteroids: III. Insights into their composition, hydration state, and structure. |journal=Icarus |date=2015 |volume=245 |pages=38–55 | doi=10.1016/j.icarus.2014.09.016|bibcode=2015Icar..245...38S }}</ref>
|-
| Comet P/2005 JQ5
| 0.02 <ref>{{cite journal |last1=Harmon |first1=J. K. |display-authors=etal |title=Radar observations of Comet P/2005 JQ5 (Catalina) |journal=Icarus |date=2006 |volume=184 |issue=1 |pages=285–288 |doi=10.1016/j.icarus.2006.05.014|bibcode=2006Icar..184..285H }}</ref>
|}
The values reported for the Moon, Mercury, Mars, Venus, and Comet P/2005 JQ5 are derived from the total (OC+SC) radar albedo reported in those references.

====Relationship to surface [[bulk density]]====
In the event that most of the echo is from first surface reflections (<math>\hat{\sigma}_\text{OC} < 0.1</math> or so), the OC radar albedo is a first-order approximation of the Fresnel reflection coefficient (aka reflectivity)<ref name="Ostro_Asteroid_Radar" /> and can be used to estimate the bulk density of a planetary surface to a depth of a meter or so (a few wavelengths of the radar wavelength which is typically at the decimeter scale) using the following empirical relationships:<ref name="Shepard_M2">{{cite journal |last1=Shepard |first1=M. K. |display-authors=etal |title=A radar survey of M- and X-class asteroids II. Summary and synthesis |journal=Icarus |date=2010 |volume=208 |issue=1 |pages=221–237 |doi=10.1016/j.icarus.2010.01.017|bibcode=2010Icar..208..221S }}</ref>

:<math>\rho = \begin{cases}
   3.20 \text{ g cm}^{-3} \ln \left( \frac{1 + \sqrt{0.83 \hat{\sigma}_\text{OC}}}{1 - \sqrt{0.83 \hat{\sigma}_\text{OC}}} \right) & \text{for } \hat{\sigma}_\text{OC} \le 0.07 \\
  (6.944 \hat{\sigma}_\text{OC} + 1.083) \text{ g cm}^{-3} & \text{for } \hat{\sigma}_\text{OC} > 0.07
\end{cases}</math>.

== History ==
The term albedo was introduced into optics by [[Johann Heinrich Lambert]] in his 1760 work ''[[Photometria]]''.<ref>{{Cite journal |last=Perkins |first=Sid |date=2019-12-17 |title=Albedo is a simple concept that plays complicated roles in climate and astronomy |journal=Proceedings of the National Academy of Sciences |volume=116 |issue=51 |pages=25369–25371 |doi=10.1073/pnas.1918770116|doi-access=free |pmid=31848298 |pmc=6926063 }}</ref>

==See also==
<!-- Please keep entries in alphabetical order & add a short description [[WP:SEEALSO]] -->
{{Div col|colwidth=20em}}
* [[Bio-geoengineering]]
* [[Cool roof]]
* [[Daisyworld]]
* [[Emissivity]]
* [[Exitance]]
* [[Global dimming]]
* [[Ice–albedo feedback]]
* [[Irradiance]]
* [[Kirchhoff's law of thermal radiation]]
* [[Opposition surge]]
* [[Polar see-saw]]
* [[Radar astronomy]]
* [[Solar radiation management]]
{{div col end}}
<!-- please keep entries in alphabetical order -->

==References==
{{Reflist|refs=
<ref name="Goode">{{Cite journal |last=Goode |first=P. R. |date=2001 |title=Earthshine Observations of the Earth's Reflectance |journal=[[Geophysical Research Letters]] |volume=28 |issue=9 |pages=1671–1674 |url=http://www.agu.org/journals/ABS/2001/2000GL012580.shtml |doi=10.1029/2000GL012580 |bibcode = 2001GeoRL..28.1671G |s2cid=34790317 |display-authors=etal}}</ref>

<ref name="NASA">{{cite web|url=http://modis.gsfc.nasa.gov/data/atbd/atbd_mod09.pdf|title=MODIS BRDF/Albedo Product: Algorithm Theoretical Basis Document, Version 5.0|access-date=2 June 2009| archive-url= https://web.archive.org/web/20090601063932/http://modis.gsfc.nasa.gov/data/atbd/atbd_mod09.pdf| archive-date= 1 June 2009<!--Added by DASHBot-->}}</ref>

<ref name="washington">{{cite web|url=http://www.atmos.washington.edu/~sgw/PAPERS/2002_Snowball.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www.atmos.washington.edu/~sgw/PAPERS/2002_Snowball.pdf |archive-date=2022-10-09 |url-status=live|title=Snowball Earth: Ice thickness on the tropical ocean|website=atmos.washington.edu|access-date=20 September 2009}}</ref>

<ref name="clim-past">{{cite web|url=http://www.clim-past.net/2/31/2006/cp-2-31-2006.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www.clim-past.net/2/31/2006/cp-2-31-2006.pdf |archive-date=2022-10-09 |url-status=live|title=Effect of land albedo, CO<sub>2</sub>, orography, and oceanic heat transport on extreme climates|website=Clim-past.net|access-date=20 September 2009}}</ref>

<ref name="Smith Robin">{{cite web|url=http://www.mpimet.mpg.de/fileadmin/staff/smithrobin/IC_JClim-final.pdf|title=Global climate and ocean circulation on an aquaplanet ocean-atmosphere general circulation model|access-date=20 September 2009| archive-url= https://web.archive.org/web/20090920212836/http://www.mpimet.mpg.de/fileadmin/staff/smithrobin/IC_JClim-final.pdf| archive-date= 20 September 2009<!--Added by DASHBot-->}}</ref>
<ref name="medkeff">{{cite web
| url         = http://jeff.medkeff.com/astro/lunar/obs_tech/albedo.htm
| title       = Lunar Albedo
| first       = Jeff
| last        = Medkeff
| author-link  = Jeffrey S. Medkeff
| date        = 2002
| archive-url  = https://web.archive.org/web/20080523151225/http://jeff.medkeff.com/astro/lunar/obs_tech/albedo.htm
| archive-date = 23 May 2008
| access-date  = 5 July 2010
}}
</ref>

<!-- <ref name="Dickinson">{{cite journal | last1 = Dickinson | first1 = R. E. | last2 = Kennedy | first2 = P. J. | date = 1992 | title = Impacts on regional climate of Amazon deforestation | journal = Geophys. Res. Lett. | volume = 19 | pages = 1947–1950 | doi=10.1029/92gl01905 | bibcode=1992GeoRL..19.1947D}}</ref> -->

<!-- <ref name="mit">[http://web.mit.edu/12.000/www/m2006/final/characterization/abiotic_water.html http://web.mit.edu/12.000/www/m2006/final/characterization/abiotic_water.html] Project Amazonia: Characterization – Abiotic – Water</ref> -->

<ref name="mmutrees">{{cite web|url=http://www.ace.mmu.ac.uk/Resources/gcc/1-3-3.html |archive-url=https://web.archive.org/web/20030301133707/http://www.ace.mmu.ac.uk/Resources/gcc/1-3-3.html |url-status=dead |archive-date=1 March 2003 |title=The Climate System |publisher=Manchester Metropolitan University |access-date=11 November 2007 }}</ref>

<ref name="Betts">{{cite journal | doi = 10.1038/35041545 | date = 2000 | last1 = Betts | first1 = Richard A. | journal = Nature | volume = 408 | issue = 6809 | pages = 187–190 | pmid = 11089969 | title = Offset of the potential carbon sink from boreal forestation by decreases in surface albedo |bibcode = 2000Natur.408..187B | s2cid = 4405762 }}</ref>

<ref name="Fresnel">{{cite web|url=http://vih.freeshell.org/pp/01-ONW-St.Petersburg/Fresnel.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://vih.freeshell.org/pp/01-ONW-St.Petersburg/Fresnel.pdf |archive-date=2022-10-09 |url-status=live |title=Spectral Approach To Calculate Specular reflection of Light From Wavy Water Surface |publisher=Vih.freeshell.org |access-date=16 March 2015}}</ref>

<ref name="BlueskyAlbedo">{{Cite journal |last=Roman |first=M. O. |author2=C.B. Schaaf|author3=P. Lewis|author4=F. Gao|author5=G.P. Anderson|author6=J.L. Privette|author7=A.H. Strahler|author8=C.E. Woodcock|author9=M. Barnsley |date=2010 |title=Assessing the Coupling between Surface Albedo derived from MODIS and the Fraction of Diffuse Skylight over Spatially-Characterized Landscapes |journal=Remote Sensing of Environment |volume=114 |pages=738–760 |doi=10.1016/j.rse.2009.11.014 |issue=4  |url=https://www.academia.edu/406124|bibcode = 2010RSEnv.114..738R }}</ref>

<ref name="Mallama_et_al">{{cite journal |title=Comprehensive wide-band magnitudes and albedos for the planets, with applications to exo-planets and Planet Nine |journal=Icarus |first1=Anthony |last1=Mallama |first2=Bruce |last2=Krobusek |first3=Hristo |last3=Pavlov |volume=282 |pages=19–33 |date=2017 |doi=10.1016/j.icarus.2016.09.023 |bibcode=2017Icar..282...19M |arxiv=1609.05048 |s2cid=119307693 }}</ref>

<ref name="Mallama">{{cite arXiv |title=The spherical bolometric albedo for planet Mercury |first=Anthony |last=Mallama |date=2017 |class=astro-ph.EP |eprint=1703.02670}}</ref>

<ref name="Haus_et_al">{{cite journal |title=Radiative energy balance of Venus based on improved models of the middle and lower atmosphere |journal=Icarus |first1=R. |last1=Haus|display-authors=et al |volume=272 |pages=178–205 |date=July 2016 |doi=10.1016/j.icarus.2016.02.048 |bibcode=2016Icar..272..178H |url=https://elib.dlr.de/109285/1/Haus%20et%20al%202017_ICARUS.pdf |archive-url=https://ghostarchive.org/archive/20221009/https://elib.dlr.de/109285/1/Haus%20et%20al%202017_ICARUS.pdf |archive-date=2022-10-09 |url-status=live }}</ref>

<ref name="Li_et_al">{{cite journal |title=Less absorbed solar energy and more internal heat for Jupiter |first1=Liming |last1=Li|display-authors=et al |journal=Nature Communications |volume=9 |issue=1 |page=3709 |date=2018 |doi=10.1038/s41467-018-06107-2 |pmid=30213944 |pmc=6137063 |bibcode=2018NatCo...9.3709L }}</ref>

<ref name="Hanel_et_al">{{cite journal |title=Albedo, internal heat flux, and energy balance of Saturn |first1=R.A. |last1=Hanel|display-authors=et al |journal=Icarus |volume=53 |issue=2 |pages=262–285 |date=1983 |doi=10.1016/0019-1035(83)90147-1 |bibcode=1983Icar...53..262H }}</ref>

<ref name="Pearl_et_al_Uranus">{{cite journal |title=The albedo, effective temperature, and energy balance of Uranus, as determined from Voyager IRIS data |first1=J.C. |last1=Pearl|display-authors=et al |journal=Icarus |volume=84 |issue=1 |pages=12–28 |date=1990 |doi=10.1016/0019-1035(90)90155-3 |bibcode=1990Icar...84...12P }}</ref>

<ref name="Pearl_et_al_Neptune">{{cite journal |title=The albedo, effective temperature, and energy balance of Neptune, as determined from Voyager data |first1=J.C. |last1=Pearl|display-authors=et al |journal=J. Geophys. Res. |volume=96 |pages=18,921–18,930 |date=1991 |doi=10.1029/91JA01087 |bibcode=1991JGR....9618921P }}</ref>

}}

==External links==
{{wiktionary}}
* [https://sites.google.com/site/albedoproject/home Albedo Project] {{Webarchive|url=https://web.archive.org/web/20190403112715/https://sites.google.com/site/albedoproject/home |url2=https://archive.wikiwix.com/cache/20240303205102/https://sites.google.com/site/albedoproject/home |date=3 April 2019 |date2=3 March 2024 }}
* [http://www.eoearth.org/article/Albedo Albedo – Encyclopedia of Earth]
* [https://web.archive.org/web/20060505132944/http://www-modis.bu.edu/brdf/product.html NASA MODIS BRDF/albedo product site]
* [https://drive.google.com/drive/folders/1bVUcTBiZ1B7KhcnYeJiz-zFmpzGtrele?usp=sharing Ocean surface albedo look-up-table]
* [https://web.archive.org/web/20081125082044/http://www.eumetsat.int/Home/Main/Access_to_Data/Meteosat_Meteorological_Products/Product_List/SP_1125489019643?l=en Surface albedo derived from Meteosat observations]
* [https://web.archive.org/web/20080523151225/http://jeff.medkeff.com/astro/lunar/obs_tech/albedo.htm A discussion of Lunar albedos]
* [http://www.tvu.com/metalreflectivityLR.jpg reflectivity of metals (chart)] {{Webarchive|url=https://web.archive.org/web/20160304024228/http://www.tvu.com/metalreflectivityLR.jpg |date=4 March 2016 }}

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